Heretofore, greenhouses referred to as vinyl houses or pipe houses have been used so as to enable the growth environment for plants to be controlled when growing plants. This type of agricultural house is used for the purpose of forming a growth environment appropriate for plants by enabling the plant growth environment such as temperature, humidity, light intensity, and the like to be managed while incorporating an external environment by enabling sunlight to enter.
Although, with this type of agricultural house, it has been conceived to have a pipe line for passing a heating medium such as warm water or cold water installed inside the agricultural house in order to manage the temperature of the internal space, there is a problem in that cost increases since a facility for controlling the temperature is required in addition to facilities for watering and ventilation.
On the other hand, in view of the fact that the agricultural house is configured by a frame, which is a structural material, and a covering material to cover the frame, a configuration has been proposed in which an outside surface of the covering material is a hydrophilic-treated surface, and water is made to flow down the outside surface (refer to JP 2007-300836A (hereinafter referred to as “Document 1”), for example). It is described in Document 1 that an effect of suppressing temperature increase inside the agricultural house during the daytime and suppressing temperature decrease during the night can be obtained by causing water to flow on the outer surface of the covering material.
The technique described in Document 1 can conceivably be implemented with a low facility cost compared with a configuration in which a pipe line is provided for passing warm water or cold water only for adjusting an internal temperature of the agricultural house. However, since a watering apparatus for causing water to flow down the outside surface of the agricultural house is required, a facility other than facilities for watering plants and for ventilating the agricultural house is still required. Moreover, the water that flows down the outside surface of the agricultural house is required separately from the water for watering plants, and thus there is a problem in using water only for temperature adjustment in that running costs increase even though a water amount used for this purpose is relatively small.
In particular, since the market price of delicate vegetables such as spinach, komatsuna, and mizuna is relatively low, it could become unprofitable if facility costs or running costs increase. Therefore, it is desired to suppress facility costs and running costs while enabling the growth environment for plants to be controlled.
If temperature control for plants becomes possible at a low cost, plants that are mainly cultivated in the winter could be cultivated in the summer, and plants that are mainly cultivated in the summer could be cultivated in the winter. As a result, it can be expected that the earning rate will improve by increasing the turnover rate of plant cultivation, and that high selling prices will be obtained by shipping in periods of short supply.